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Section
II.
WHAT
ARE THE BIOLOGIC PROPERTIES OF SILVER RELATED TO WOUND
INFECTION CONTROL AND HEALING
(THE FACTS ABOUT SILVER)
Silver has long
been known to be a potent antimicrobial agent and its
beneficial effects on wound biology have in general been
overlooked until recently. A description of what silver does
and its role in wound management will be presented briefly
with a more complete discussion in later sections.
ANTIMICROBIAL
PROPERTIES:
The
antimicrobial activity of silver ion is well defined. Silver
ion rapidly kills microbes by blocking the cell respiration
pathway. The speed of action is almost instantaneous once
the silver reaches the microbe. The efficacy of microbe
killing is based not only on the amount of silver ion
present, but likely also the presence of other silver
radicals generated by a silver releasing product.
Because of
mechanism of action, microbial resistance to silver itself
has not been reported. In addition, silver has repeatedly
been shown to be non-toxic to human cells. Toxicity occurs
from the complexes used to deliver silver such as nitrate
and sulfadiazine.
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Infection
Control ( Antimicrobial Properties )
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kills
microbes on contact by poisoning microbe
cellular respiration
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speed
of action directly correlated with the silver
ion dose in contact with microbes
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silver
resistance is not seen
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safe
and non-allergenic
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Silver
ion is known to have the following biochemical
effects on a wound:
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Histologically
decreases wound surface inflammation
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Decreases
wound surface excess metalloproteinase activity
likely by decreasing zinc, essential for
metalloproteinase (MMP) activity
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Oxidizes
and binds to sulfur bonds, unlike Zinc and
Copper which bind to oxygen. Sulfur bonds are
necessary for MMP activity
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Increase
in wound calcium (a pro epithelialization
effect)
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Wound Healing Properties:
The
anti-inflammatory effects of silver ion on a wound have been
recognized for centuries. Most of the reports are purely
descriptive in nature identifying the decrease in erythema and
increased healing.
A number of the
biochemical effects of silver on the wound have been
documented over a decade ago. However, only recently with the
new concepts on wound healing and healing impairment, can a
mechanism of action be presented. The major focus of wound
healing has been on the relationship between tissue
destruction by a group of collagenase enzymes known as
METALLOPROTEINASES (MMP) and tissue synthesis which is
stimulated by growth factors.
CURRENT
CONCEPTS
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An
excess of MMP activity has been reported in burn
wounds and in chronic wounds.
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Action
of the MMP’s is dependent on the availability of
free Zinc.
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Silver
decreases surface Zinc which could decrease excess MMP
activity and increasing healing rate.
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Recent
findings indicate that silver (as delivered by the
pure silver system ACTICOAT) decreases MMP activity.
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The
fact that silver increases wound surface calcium
should stimulate epithelialization.
A
more detailed description will be presented later.
Wound
Healing (Wound Surface Effects)
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decreases
wound surface excess inflammation (anti-inflammatory)
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decreases
metalloproteinase MMP activity present which is
excessive in burns and chronic wounds likely by
decreasing zinc
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increases
wound calcium - a pro healing effect
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ACTION
OF SILVER ION ON BURN WOUND
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Effect
of silver delivery (ACTICOAT) on Metalloproteinase (Collagenase)
MMP 1.8.13
A quantitative
assay was undertaken using collagenase MMP-1, MMP-8; and
MMP-13). As MMP-2 and MMP-9 have related activities (gelatinase),
they are anticipated to behave similarly and produce results
similar to those obtained for the collagenase tested.
The collagenase
inhibition test was conducted by adding dilutions of
ACTICOAT dressing extract (3 sq. in. in 5 ml. Water) to an
assay mixture containing fluorescently-labeled gelatin and
appropriately diluted (in water) collagenase. Following
incubation the activity of the enzyme was compared to
baseline activity (no inhibitor). The assay was also
conducted in the presence of a known inhibitor (0.5 mM
phenanthroline). The inhibitor reduced enzyme activity by
70%. The silver related from ACTICOAT reduced enzyme
activity by 90%.
  
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